A conventional focusing method is adapted for an image capturing device provided in a mobile device, such as a cell phone or a tablet computer. The image capturing device includes an image sensor, a lens module, a focus driver and a processor module. The focusing method is implemented through the adoption of contrast detection technology. The processor module first receives image data which is generated by the image sensor that detects an image of an object. The processor then obtains contrast of image data according to the image data received from the image sensor. The focus driver is controlled to drive movement of the lens module for controlling a distance between the lens module and the image sensor, so as to obtain image data having relative maximum contrast. Based on the conventional focusing method, if a distance between the object and the lens module is very small, such as smaller than 30 centimeters, in order to obtain the image data with relative maximum contrast, the lens module which is driven by the focus driver is required to be moved repeatedly. In this way, a longer focusing time is needed, and higher power consumption is inevitable.